Indirect air-side economizer for removing heat from enclosed spaces with high internal heat generation

ABSTRACT

An Indirect Air-Side Economizer based around an air-to-air heat exchanger is provided that is advantageously operated in conjunction with other components in an integrated system to facilitate necessary rejection of heat and certain removal of particulate from the air within a data center. The disclosed device may include separate cooling methodologies that can be operated independently to cool return air from that data center.

This application is related to, and shares a common disclosure with,U.S. patent application Ser. No. ______ (Attorney Docket No. 146998)filed Dec. 30, 2010, U.S. patent application Ser. No. ______ (AttorneyDocket No. 147000) filed Dec. 30, 2010, and U.S. patent application Ser.No. ______ (Attorney Docket No. 147001) filed Dec. 30, 2010.

BACKGROUND

This disclosure is directed to systems and methods for removing heatfrom recirculated air from an enclosed space, particularly from a datacenter, in an efficient and effective manner.

Data centers include data servers and other ancillary equipment. Thedata centers draw significant amounts of power and generate significantamounts of heat. Cooling the data centers, particularly as they haveincreased in size and electronic capacity, has become an increasingchallenge. Cooling the data centers economically is an even greaterchallenge.

Computer servers have typically been cooled by air-conditioned,refrigerated air that is delivered into the data centers by allavailable means, including through the elevated flooring, toindividually cool each computer server. The requirement for providing55° F. to 65° F. refrigerated cold air was understood industry widebased on the need to minimize the potential for hot spots within thedata servers. Providing the required amount of refrigerated cold air, asthe server banks increased in size, proved increasingly costly andcomplex.

Creative air management methodologies have been undertaken to remove thegenerated heat in a more efficient manner. These include construction ofspecific air pathways with segregated, enclosed cold air supply aisles(“cold aisles”) and separate hot air return aisles (“hot aisles”) withindata centers in an attempt to keep from commingling cold air with hotair in an open space. Such construction aids in providing necessarycooling capacity more economically and reduces the potential for serverhot spots.

A significant change to the parameters for cooling data centers wasrealized when the industry determined that warmer server-inletconditions for Class I and II data centers was acceptable. That,combined with advances in hot and cold aisle containment systems anddesigns, permits data center cooling units to deliver warmer air to coolthe servers than previously thought possible. In 2008, an expandedenvelope for air conditions entering the servers in data centers wasapproved, bringing the maximum recommended server inlet temperature upto 80.6° F. The above change in recommended inlet air temperature forthe data servers caused engineers to seek new energy efficient solutionsto manage the thermal loads in the data centers.

An objective is to provide inlet air to the servers at a temperaturethat is within the recommended range while consuming the least amount oftotal power. A number of methodologies have been attempted. Some ofthese methodologies are discussed briefly below. Prior to a discussionof any individual methodology, however, it should be noted that any aircooling solution for data centers should also provide for humiditycontrol of the space in order to limit the negative effects of extremehumidity deviations within the space. Also, the air flow cannot be on acompletely closed loop because, even in the cleanest data centerenvironment, operation of the data servers themselves creates certainbyproducts that need to be diluted with some minimum level ofventilation air and/or filtered out of the air flow on a routine basis.

The following is a non-exhaustive list of methodologies that have beenattempted.

Air-Side Economizers (ASEs) simply deliver outdoor air, mixed withreturn air when required to achieve the target air delivery temperature,when ambient conditions favor free cooling, through the data center. Ashortfall of ASEs, however, is that they cannot generally be used underhot or humid ambient conditions. Thus, un-augmented ASEs provide littleability to reduce the necessary size of supplemental refrigeration-basedcooling and offer no reduction in peak electrical load. Use of ASEs alsooften leads to wide swings in space humidity unless humidificationcontrol systems are employed.

Direct Evaporative Cooling (DEC) can be used to complement ASEs toextend the operating envelope of ambient conditions for the ASEs.

Separate Water-Side Economizers may be used in which cooling towers orfluid coolers are employed in a variety of design configurations toreject some or all of the heat from the data center in combination withrefrigeration-based cooling.

Various combinations of the above methods have been attempted.

Finally, Liquid-Cooled Enclosures, sometimes referred to as in-row orin-rack cooling, may be provided in which cool water produced from acombination of chillers and cooling towers, or otherwise byrefrigerants, is pumped to heat changers or cold plates installeddirectly within server racks.

While these systems result in energy savings compared to traditional100% refrigeration-based approaches, each is less than ideal. Among theshortfalls of these systems are: (1) the need to include substantialpre-filters and post filters, particularly on systems implementing ASEs;(2) the need to modulate damper systems and relief fans or barometricdampers and pressure controls on any system that introduces outdoor airdirectly into the data center; (3) ongoing extensive reliance on chilledwater and/or condenser water piping or refrigerant piping; (4) redundantpumps; and (5) other additional support systems. These systems are oftenmaintenance intensive.

SUMMARY

It would be advantageous, in view of the above discussion, to provide anefficient and economical cooling system for a data center based onrejecting the heat from 100% recirculation air from the data center, anddelivering the air at 75° F. to 80.6° F. (or warmer as allowed by theservers utilized within the data center, and as necessary to minimizeoverall electrical power consumption).

The systems and methods according to this disclosure provide a uniquecapability using Indirect Evaporative Cooling technology to providerecirculated clean, humidity-controlled, cooled air to the inlets ofservers in a data center.

The systems and methods according to this disclosure provide a pluralityof Indirect Air-Side Economizers (IASEs) that include air-to-air heatexchangers.

In general, the systems and methods according to this disclosure areintended, among other objectives, to: (1) reduce refrigeration capacityunder all ambient conditions in most climates; (2) reduce the need forfiltration of the air used in the heat rejection process, and (3)eliminate modulating dampers and complex controls, while cooling the hotaisle air from the data center to a target air delivery temperatureusing little or no supplemental refrigeration based cooling for mostannual operating hours in most environments.

The systems and methods according to this disclosure will tend to avoidattendant shortfalls of, for example, introducing air pollutants fromoutdoor air into the data center by the heat rejection equipment, orotherwise introducing outdoor air with extreme high or low humiditylevels that could accelerate corrosion of circuit boards or lead toshort circuiting or electrostatic discharge concerns within the datacenter.

The systems and methods according to this disclosure operate incoordination with data centers configured according to availabletechnologies to include cold air corridors/galleries or cold aisles, andhot air plenums or hot aisles, as discussed briefly above, that aresegregated from each other within the data center.

The systems and methods according to this disclosure provide multipleIASE cooling units, as required to reject the heat load and meet theredundancy requirements, that provide supply air to the cold aisles ofthe data center at the target air delivery condition and recover returnair from the hot aisles for heat removal and recirculation via themultiple IASE cooling units.

The systems and methods according to this disclosure provide for avolumetric flow of air produced by multiple IASE cooling units at a rateas required to reject the heat load generated by the servers with theoperating temperature difference between the hot and cold aisles. Thevolume of air moved by the multiple IASE cooling units may be as much as200 or more air exchanges in the data center per hour.

The systems and methods according to this disclosure may include aseparate Side Stream Filtration Unit (SSFU) in which one or morefiltration units is provided to limitedly filter the recirculating airwithin the data center. The SSFU is designed and sized specifically tocirculate a portion of the recirculating air, for example, at a rate of6 to 10 exchanges of air per hour, through the SSFU and back to thereturn or supply air within the data center.

The systems and methods according to this disclosure may include aseparate Make-Up Air/Humidification Unit (MUA/HU) and Make-Up AirDehumidification/Humidification Unit (MUAD/HU) by which ventilation airis introduced into the overall air handling path in the data center,either directly or via the SSFU. The MUA/HU or MUAD/HU need only operateat a rate to introduce appropriately humidified or dehumidified ambientair into the overall air-handling path at a rate as required to achievegood air quality, humidity, and pressure control. This amount may be aslittle as 0.25 air exchanges per hour.

The systems and methods according to this disclosure substantiallyeliminate the need for extensive filtering of the recirculated air. Thislimits, for example, the extent to which the SSFU needs to be present toprovide filtration capacity. A benefit of the systems and methodsaccording to this disclosure is this reduction in filtrationrequirements, and the associated impact on supply fan motor power andmaintenance costs. In the systems and methods according to thisdisclosure filters and/or filtration units are limitedly provided, asappropriate, in the SSFU or otherwise, that do not impede the totalvolumetric flow rate of air through the data center, while providing anecessary level of filtration specifically sized to afford appropriateparticulate removal in the overall air handling system. Specifically,the quantity of filters is often reduced by a factor of 10 or so, butthe degree of filtration may be improved by utilizing a higherefficiency filtration methodology.

The systems and methods according to this disclosure include IASEs, alsoreferred to interchangeably as Recirculation Air Cooling Units (RACUs),that may specifically improve upon conventional indirect evaporativecooling systems by providing preferably one of an engineered polymerictube-type air-to-air heat exchanger, a counter-flow, plate-typeair-to-air heat exchanger, various combinations of cross flow plate-typeheat exchangers, or heat pipe type air-to-air heat exchangers. In thisregard, the systems and methods according to this disclosure may provideadditional heating/cooling, humidification/dehumidification and airhandling components within one or more of the IASEs/RACUs, the SSFU, orthe MUA/HU or MUAD/HU as may be required by, or appropriate to, aspecific geographic, and therefore, climatological location of the datacenter.

The systems and methods according to this disclosure also provide acontrol scheme for controlling the temperature of the air supplied tothe data center by controlling the mass flow rate of scavenger air(ambient cooling air) drawn through the side of the heat exchangeropposite that of the recirculating air from the data center, based onambient conditions. With a polymeric-tube type air-to-air heat exchangerin the IASE/RACU, for example, outdoor scavenger air is drawn across theexterior of tubes which are wetted by recirculation or once-thru watersystems. With scavenger air flowing over the wet exterior tube surfaces,evaporative heat transfer efficiently cools the data center hot aisleair flowing through the inside of the tubes. The heat rejection processmay be controlled by varying the speed of the scavenger fan(s), and mayinclude staging fans in concert with speed modulation to minimizeoverall power consumption. The result is an energy efficient heatrejection process that is simple to control.

These and other features and advantages of the disclosed systems andmethods are described in, or apparent from, the following detaileddescription of various exemplary embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Various exemplary embodiments of the disclosed systems and methods forproviding efficient and economical cooling for a data center will bedescribed, in detail, with reference to the following drawings, wherein:

FIG. 1 illustrates a schematic diagram of an exemplary overall datacenter cooling system according to this disclosure;

FIG. 2 illustrates a basic block diagram of an Indirect Air-SideEconomizer (LASE) or Recirculation Air Cooling Unit (RACU) according tothis disclosure;

FIG. 3 illustrates a schematic diagram of a first exemplary embodimentof an IASE/RACU according to this disclosure;

FIG. 4 illustrates a schematic diagram of a second exemplary embodimentof an IASE/RACU according to this disclosure;

FIG. 5 illustrates a cross-section depicting a sample counter flow airflow of the air in the plate-type heat exchanger depicted in the secondexemplary embodiment of the IASE/RACU shown in FIG. 4;

FIG. 6 illustrates a third exemplary embodiment of an IASE/RACU usingpolymer tubes in the air-to-air heat exchanger according to thisdisclosure;

FIG. 7 illustrates an exemplary roof-top distribution of a plurality ofIASEs/RACUs according to this disclosure;

FIG. 8 illustrates a schematic diagram of an exemplary embodiment of aSide Stream Filtration Unit (SSFU) according to this disclosure;

FIG. 9 illustrates a schematic diagram of a first exemplary embodimentof a Make-Up Air Humidification Unit (MUA/HU) according to thisdisclosure;

FIG. 10 illustrates a plan view schematic diagram of a second exemplaryembodiment of a Make-Up Air Dehumidification/Humidification Unit(MUAD/HU) in a first operating mode according to this disclosure;

FIG. 11 illustrates a plan view schematic diagram of the secondexemplary embodiment of the MUAD/HU shown in FIG. 10 in a secondoperating mode according to this disclosure;

FIG. 12 illustrates an elevation view schematic diagram of the secondexemplary embodiment of the MUAD/HU shown in FIG. 10 according to thisdisclosure;

FIG. 13 illustrates a schematic diagram of a third exemplary embodimentof an IASE/RACU design including a vertical dual cross-flow plate-typeheat exchanger arrangement according to this disclosure;

FIG. 14 illustrates a schematic diagram of a fourth exemplary embodimentof an IASE/RACU design including a horizontal dual cross-flow plate-typeheat exchanger arrangement according to this disclosure;

FIG. 15 illustrates a schematic diagram of a fifth exemplary embodimentof an IASE/RACU design including a vertical counter flow plate-type heatexchanger arrangement according to this disclosure;

FIG. 16 illustrates a schematic diagram of a sixth exemplary embodimentof an IASE/RACU design including a horizontal heat pipe heat exchangerarrangement according to this disclosure; and

FIG. 17 illustrates a schematic diagram of a seventh exemplaryembodiment of an IASE/RACU design including a vertical heat pipe heatexchanger arrangement according to this disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

The systems and methods for providing efficient and economical coolingair capabilities to data centers according to this disclosure willgenerally refer to this specific utility for those systems and methods.The exemplary embodiments described and depicted in this disclosureshould not be interpreted as being specifically limited to anyparticular configuration, or to any particular intended use. In fact,any high heat-producing environment that would benefit from an air flowcooling system according to the systems and methods of this disclosureis contemplated.

The principles of indirect evaporative cooling technology, as is used inthe disclosed embodiments of the Indirect Air-SideEconomizers/Recirculation Air Cooling Units (IASEs/RACUs) described inthis disclosure will be briefly discussed. In the disclosed IASE/RACUinstallation, outdoor scavenger air (OS/A) enters the IASE/RACU throughan inlet and flows through one side of an air-to-air heat exchanger, theOS/A-E/A (exhaust air) side. Warm return air (R/A) from the environmentwhich the IASE/RACU supports such as, for example, a data center, andspecifically the return air from a hot aisle, enters the IASE/RACU fromanother inlet and flows separately through an opposite side of theair-to-air heat exchanger, the R/A-S/A (supply air) side. The R/A-S/Aside and the OS/A-E/A side are completely separated from one another byone of a number of different methodologies. These methodologies mayinclude sealed heat exchanger plates and/or sealed heat exchangertubing, or separating partitions. As the hot aisle R/A flows through theair-to-air heat exchanger, it transfers its heat to the cooler OS/Athrough the surface that completely separates and segregates the twoairstreams. The OS/A may be used at its ambient temperature, or may beotherwise evaporatively cooled, either prior to entering the air-to-airheat exchanger or by direct spray of water onto the OS/A-E/A surfaces ofthe heat exchanger. Use of evaporative pre-cooling may enhance the heatrejection potential, particularly in instances where the OS/A has aWet-Bulb Depression (WBD, which is a difference between the dry-bulb andwet-bulb temperature) of 10° F. or more. A water-side economizer coil,piped to an external cooling tower, may be installed, for example,upstream of the direct evaporative cooler, providing additional coolingfor the OS/A and associated heat rejection. Such a combinedIndirect-Direct-Indirect cycle may likely be only used in extreme casesbecause such an apparatus would reduce the cost benefit of theun-augmented IASE/RACU.

By selecting a heat exchanger with an effectiveness of, for example,80%, and employing a 95% efficient direct evaporative pre-cooler, mostof the heat generated from a data center may be efficiently andeconomically rejected to ambient air through the heat exchanger of theIASE/RACU, even during hot and humid ambient conditions. Given a 100° F.hot aisle temperature, and a 75° F., target cold aisle temperature,whenever an outdoor air dry-bulb temperature is 68.4° F. or lower, theIASE/RACU cycle can reject 100% of the heat generated by the datacenter. This is true even in consideration of a temperature rise(nominally 1.5° F.) across the recirculating fans in the IASE/RACU.Similarly, when a 95% efficiency OS/A evaporative pre-cooler isincluded, 100% of heat generated by the data center—may be rejected bythe augmented IASE/RACU if the ambient wet-bulb temperature is 65° F. orlower, regardless of how hot the corresponding ambient dry-bulbtemperature may be.

Exemplary computations are shown below in Table 1 for an example 80%effective counter flow plate-type heat exchanger, IASE/RACU systemcooling a 200 kW IT load.

TABLE 1 Scavenger HX Pressure Scavenger Air Entering HX Air Drop Wet-Leaving HX Scavenger- Supply Air Dry-Bulb Bulb Flow Dry-Bulb SideLeaving HX* (° F.) (° F.) CFM (° F.) inches-wc Dry-Bulb (° F.) 90 8528000 98.5 0.61 92.4 80 78 28000 95.7 0.63 84.4 70 69 28000 92.8 0.6576.3 65 64 22500 94.4 0.44 75 60 59 18100 96.3 0.30 75 50 49 13350 98.30.18 75 40 39 10665 99.3 0.12 75 30 29 8875 99.9 0.09 75 20 19 7580100.3 0.07 75 10 9 6585 100.6 0.06 75 0 −1 5800 100.8 0.05 75 −10 −115160 100.9 0.04 75 −20 −20.5 4625 101.0 0.03 75 −30 −30.5 4175 101.10.03 75 Supply Airflow entering HX = 26,760 ACFM HX Pressure Drop(Supply-Side) = 0.56 inches-wc *Scavenger Air Flow Controlled toMaintain Target Supply Air Dry-Bulb = 75° F.

It should be noted that the required OS/A flow decreases rapidly withdecreasing ambient dry-bulb entering temperature. At, for example, anambient dry-bulb temperature of only 50° F., the OS/A flow drops by morethan 50% (to 13,350 CFM) from a designed OS/A flow. This allows for areduction in the outdoor scavenger fan motor power to approximately 12%of its design maximum.

Table 2 below shows, for various U.S. cities, the annual hours in atypical year where an 80% effective plate-type heat exchanger augmentedwith a 95% efficient scavenger air evaporative pre-cooler can cool hotaisle air, after fan heat, from 101.5° F. to 75° F.

TABLE 2 City Hours % of Annual Hrs Albuquerque, NM 8759 99.99% Atlanta,GA 6943 79.26% Baltimore, MD 7416 84.66% Boise, ID 8760 100.00% Boston,MA 8302 94.77% Chicago, IL 8085 92.29% Boulder, CO 8759 99.99% FortWorth, TX 5937 67.77% Las Vegas, NV 8474 96.74% Los Angeles, CA 869799.28% Minneapolis, MN 8104 92.51% Phoenix, AZ 7391 84.37% Portland, OR8742 99.79% Salt Lake City, UT 8758 99.98% San Francisco, CA 8755 99.94%Seattle, WA 8755 99.94% * allows for 1.5° F. of fan heat

The systems and methods according to this disclosure are designed andimplemented with the above parameters in mind.

A. Overall System Configuration

For consistency, throughout this disclosure, the different depicted airflows will be referred to as: (1) supply air (S/A), which is the cooledair output from the IASE/RACU to the cold aisles of the data center; (2)return air (R/A), which is the air returned to the IASE/RACU from thehot aisles in the data center; (3) outdoor scavenger air (OS/A), whichis the air input to the IASE/RACU from outside to the air-to-air heatexchanger in the IASE/RACU; and (4) exhaust air (E/A), which is the airforcibly exhausted from the IASE/RACU as the OS/A has passed through theair-to-air heat exchanger for heat extraction. It should be noted thatOS/A will also be input to the Make-Up Air/Humidification Unit (MUA/HU)or Make-Up Air Dehumidification/Humidification Unit (MUAD/HU). Forcompleteness, reference will be made to auxiliary air (A/A) output fromthe MUA/HU or MUAD/HU either directly into the room or to the SideStream Filtration Unit (SSFU) and supplemental filtered air (SF/A)output from the SSFU into a flow path including R/A to be supplied as anaugment to the R/A returning to the IASE/RACU.

FIG. 1 illustrates a schematic diagram of an exemplary overall datacenter cooling system according to this disclosure. As shown in FIG. 1,a system for removing heat from a data center 100 includes severalintegrated components. These components include, for example, aplurality of IASEs/RACUs 110, at least one MUAD/HU 130 and at least oneSSFU 140. The combination of these units controls the flow of S/A to thecold aisles 115A-D in the data center to support cooling, particulateremoval, dilution of room generated contaminants by introducing filteredventilation air, and humidity control of the individual data servers150A-F.

In FIG. 1, S/A provided to the cold aisles 115A-D is forced through thedata servers 150A-F (see Arrows A entering the data servers and Arrows Bleaving the data servers) where the cooled S/A absorbs heat and exitsthe data servers into hot aisles 125A-C as R/A. The R/A is thengenerally passed through a collecting manifold in the hot aisle systemback toward the IASE/RACU units 110 generally along a path depicted as156 in FIG. 1, which may constitute a plenum or duct system. The R/Aenters the IASE/RACU 110 through an inlet opening 114 that may include adamper (not shown) for controlling flow of the R/A to the IASE/RACU 110and/or for isolating the system during maintenance.

Specific operation of the IASE/RACU 110 will be discussed in detailbelow. For the purposes of this overview, OS/A enters the IASE/RACU 110via an inlet opening, or openings; 120 that also may include an intakehood, filter, and/or damper (not shown). As will be seen in FIG. 2, OS/Athen passes through an air-to-air heat exchanger where it cools the R/Aflowing thru the other side of the air-to-air heat exchanger and exitsthe air-to-air heat exchanger as E/A via an outlet opening 116 that alsomay include a damper 119 and an exhaust port, pipe or stack 118. As willbe seen in a detailed description of the various embodiments ofIASEs/RACUs discussed below, a scavenger heat removal fan, or fans, isplaced in the OS/A-EA side to control the movement of the OS/A from theinlet opening 120 through the air-to-air heat exchanger, where itbecomes E/A, to the outlet opening 116 and out the optional exhaustport, pipe or stack 118. Each scavenger heat removal fan may include adamper 119. The exhaust port, pipe or stack 118 may be integral to theexhaust fan, as is typical of vane or tube-axial type fans.

Separately, R/A enters the IASE/RACU 110 via inlet opening 114 that mayalso include a damper (not shown), the R/A passing through theair-to-air heat exchanger, which will be described in detail below. TheR/A is cooled from non-commingled flow with the OS/A in the air-to-airheat exchanger and exits the air-to-air heat exchanger, and theIASE/RACU 110, as cold S/A via outlet opening 112, that may include adamper, to be supplied to the cold aisles 115A-D in the data center 100.

A number of IASEs/RACUs 110, of a specified air handling (throughput)capacity, may be selected to optimize the flow of S/A through the datacenter according to the above-discussed parameters and the methoddiscussed below, which include, for example, volumetric movement of theair, in the S/A (see Arrows A in FIG. 1) R/A (see Arrows B in FIG. 1)cycle through the data servers, and overall through the system at a rateof as much as 200 or more air exchanges per hour.

A Make-Up Air Dehumidification/Humidification Unit (MUAD/HU) 130 may beprovided to input A/A into the system at a specified fixed or variablerate. In the MUAD/HU 130, as will be described in greater detail below,OS/A enters through an inlet opening 132, and is filtered and/orhumidified/dehumidified, as appropriate. The OS/A is then forced by acirculating fan through outlet opening 136 to, for example, conduit 138leading to the Side-Stream Filtration Unit (SSFU) 140 that will bediscussed below, or otherwise directly into the room. A R/A pickup 152for R/A may be included to provide R/A via an inlet opening 134 of theMUAD/HU 130. R/A is used where heat may be required for efficientoperation of the humidification process of the MUAD/HU 130. Theventilation rate for air entering inlet opening 132 of the MUAD/HU 130to be supplied as A/A to the system will generally be at a relativelyminimal rate as low as approximately 0.25 air exchanges per hour.

A Side Stream Filtration Unit (SSFU) 140 may be provided to filter theR/A entering through an inlet 144. It may also be installed to provideadditional polishing filtration to A/A, introduced by the MUAD/HU 130,prior to delivery into the data center. In the SSFU 140 shown in FIG. 1,A/A from the MUAD/HU 130 enters via an inlet opening 142 from conduit138 in concert with R/A that enters via one or more inlet openings 144via one or more conduits or plenums 154, and passes through one or morefilters being forced by a separate circulating fan in the SSFU 140 (thatwill be discussed in detail below), prior to exiting the SSFU 140 via anoutlet opening 146 as SF/A. Outlet opening 146 from the SSFU 140 mayinclude a conduit 148 to the R/A path 156 so that the SF/A can be mixedwith the R/A prior to the R/A entering the IASE/RACU 110 via inletopening 114.

A purpose of the SSFU 140 is to remove impurities that are generatedwithin the data servers 150A-F, or other airborne impurities orpollutants that are entrained in the R/A stream in an effort to removeimpurities from the R/A and, when so installed, to provide polishingfiltration of the ventilation air. The turnover rate of air passingthrough the SSFU 140 according to the R/A path is preferably at a rateof approximately 6 to 10 exchanges per hour, significantly less than theair turnover rate required to reject heat from the data center.

With the above general overview of the disclosed overall air handlingsystem, individual components of the overall air handling system will bediscussed in detail with reference to exemplary embodiments below.

B. Indirect Air-Side Economizer/Recirculation Air Cooling Unit(IASE/RACU)

FIG. 2 illustrates a basic block diagram of an Indirect Air-SideEconomizer (IASE) or Recirculation Air Cooling Unit (RACU) according tothis disclosure. FIG. 2 reveals the IASE/RACU 110 shown in FIG. 1 ingreater detail. As explained above, R/A flows in through inlet opening114 toward an air-to-air heat exchanger 210 while OS/A flows throughinlet opening 120 toward air-to-air heat exchanger 210. Air-to-air heatexchange occurs in air-to-air heat exchanger 210 according to a numberof different methodologies that will be discussed as specificembodiments below. The R/A cooled by the air-to-air heat exchanger 210exits the air-to-air heat exchanger 210 and exits the IASE/RACU 110 viaoutlet opening 112 to the cold aisles 115A-D (shown in FIG. 1). The OS/Ais drawn through air-to-air exchanger 210 and exits the air-to-air heatexchanger 210 as E/A, exiting the IASE/RACU 110 via outlet opening 116and optional exhaust port, pipe or stack 118, which may be integral toan exhaust fan 136 and may also include a damper 119.

As will be described in greater detail below, plate-type air-to air heatexchangers, heat pipe air-to air heat exchangers and polymeric tubecross-flow air-to-air heat exchangers are optimal candidates for use inthe IASE/RACU applications of this disclosure. Advantages include (1)lack of measurable leakage when used according to this application, (2)no moving parts in the air-to-air heat exchanger unit itself, (3)relatively low maintenance requirements as compared to other morecomplex cooling systems designs, and (4) an ability to be specificallydesigned for increased efficiency based on their (a) ease of design andconstruction and (b) compatibility with a wide array of support unitrequirements. Finally, it should be recognized that such air-to-air heatexchangers can be designed and constructed with a variety of flowpatterns, not limited to the specific exemplary embodiments of flowpatterns that are described and depicted in this disclosure. Structuresand configurations may be implemented that prove particularly favorableto cooling a broad spectrum of data center architectures.

FIG. 3 illustrates a schematic diagram of a first exemplary embodimentof an IASE/RACU 310 according to this disclosure. As shown in FIG. 3,IASE/RACU 310 may include, for example, an R/A inlet opening 314 throughwhich R/A enters the IASE/RACU 310. A filter 340 may be provided tofilter the R/A, either before or after the R/A passes throughcirculating fan, or fans, 338. Movement of the R/A through the circuitbetween inlet opening 314 and outlet opening 312 is facilitated andforced by circulating fan(s) 338. R/A is forced by the circulatingfan(s) 338 through one side 352 of the air-to-air heat exchanger 350.The circulating fan(s) 338 is placed in the R/A side of this cyclebecause the circulating fan(s) 338 will introduce additional heat intothe moving air in the R/A-S/A side 352 of the cycle, and much of thisheat may be extracted thru the air-to-air heat exchange process.Further, installing the circulating fan(s) 338 in this blow-thruarrangement results in the air-handling system being under positivepressure relative to ambient. This positive pressure in the systemreduces the potential for dust or other particulate matter entering theR/A tunnel thru doors or other points of access. Typically, acirculating fan 338, because of air compression and motorinefficiencies, raises the temperature of the R/A pushed through it by1.5° F. or more. The R/A is cooled in the R/A-S/A side 352 of theair-to-air heat exchanger 350 and exits the air-to-air heat exchanger350 as S/A via outlet 312. An additional cooling coil 342 may beprovided to further cool the S/A as appropriate to the specificinstallation of the IASE/RACU 310. Through the action of the circulatingfan(s) 338, cool S/A is forced to exit the IASE/RACU 310 via outletopening 312 toward the cold aisles 115A-D of the data center (as shownin FIG. 1). The speed of circulating fan(s) 338 is controlled tooptimize total power consumption while achieving the desired heatrejection. The method for control may involve maintaining a slightpositive pressure gradient from server rack inlet to outlet and/orachieving the target hot-aisle temperature while ensuring that there areno excessive spikes in air temperature entering the data servers, orpreferably, having the speed signal derived from the IT equipment.

Separately, in the IASE/RACU 310, OS/A is drawn through inlet opening320 by the action of scavenger fan, or fans, 336. IASE/RACU 310 mayinclude an intake hood (not shown) and filter 332 to filter the OS/Aearly in the cycle in this side of the IASE/RACU 310. The filter 332 maywork in conjunction with, or separately from, a direct evaporativepre-cooler 334 that may be included in the OS/A path toward theair-to-air heat exchanger 350. OS/A, filtered and pre-cooled asappropriate, is then drawn through the OS/A E/A side 354 of theair-to-air heat exchanger 350 by the operation of scavenger fan, orfans, 336. Again, the scavenger fan(s) 336 is placed on the “hot” side(draw-thru side) of the scavenger air path in order that the OS/A is notpre-heated, even by as little as 1.5° F., prior to entering the OS/A-E/Aside 354 of the air-to-air heat exchanger 350. This relative positioningalso minimizes the potential for any OS/A to leak, thru any possibleflow path within the IASE/RACU 310 from the OS/A-E/A side 354 of the airhandler, over to the clean R/A-S/A side 352.

Operation of the scavenger air fan(s) 336 draws the E/A from an outletside of the OS/A-E/A side 354 of the air-to-air heat exchanger 350 andforcibly ejects the E/A via outlet opening 316 and exhaust port, pipe orstack 318, which may be an integral part of the scavenger fan(s), backto the environment. The scavenger fan(s) 336 are actively controlled,thru a combination of staging (when more than one fan is employed) andspeed modulation to provide only the flow rate of cooling air throughthe OS/A-E/A side 354 of the air-to-air heat exchanger 350 as isnecessary to cool the S/A to the target supply temperature using theleast total power possible. Staging or cycling fans, each having aback-draft damper device (not shown), results in energy savings when thetotal scavenger flow is low. This is preferable to modulating a slowspeed in all of the scavenger fans 336 because the combined motor andvariable speed device efficiency degrades as speed is reduced.

In exemplary embodiments, it is advantageous to specifically place theOS/A inlet opening 320 and the exhaust port, pipe or stack 318 at somedistance from one another in order that expelled hot, and potentiallymoist, E/A does not blend with native OS/A in a manner that may affectthe temperature or moisture level of the OS/A entering, i.e., byslightly preheating or increasing the wet bulb temperature of the OS/Aprior to the OS/A being drawn through inlet opening 320 in the IASE/RACU310.

FIG. 4 illustrates a second exemplary embodiment of an IASE/RACU 510according to this disclosure. As shown in FIG. 4, this exemplaryembodiment of the IASE/RACU 510 is based around plate-type counter flowair-to-air heat exchangers 550. The structure of this embodiment of theIASE/RACU 510 is unique in several aspects.

In this embodiment, R/A enters the IASE/RACU 510 via inlet opening 514and is moved through the system by the power of circulating fan, or fans538. Considerations for the operation of circulating fan(s) 538, and forthe placement of circulating fan(s) 538 in the IASE/RACU 510, are thesame as those discussed above with regard to inlet opening 314 andcirculating fan(s) 338 in the previous embodiment depicted in FIG. 3.R/A is then moved through air-to-air heat exchangers 550 in a counterflow manner that will be described in more detail with reference toadjacent FIG. 5. In this embodiment as well, one or more active coolingcoils 542 may be provided to further cool the S/A exiting the air-to-airheat exchangers 550 prior to exiting the IASE/RACU 510 via outletopening 512.

OS/A enters the IASE/RACU through inlet opening 520. Different from theprevious embodiments, however, the embodiment of the IASE/RACU 510 shownin FIG. 4 includes an additional inlet space, OS/A pre-cool andrefrigeration condensing section 525. In OS/A pre-cool and refrigerationcondensing section 525, a pre-filter 529 may be included. The pre-filter529 may be followed by a direct evaporative cooler 530, installed topre-condition the air used for heat rejection thru both the air-to-airheat exchanger 550 and a refrigeration condenser coil 540. Thus, thesingle direct evaporative cooler 530 may serve as a pre-cooler for boththe IASE/RACU cycle and the air-cooled condenser coils. The condenserair is pulled by condenser fan, or fans 543 thru the condenser coil 540,where the heat of compression from the supplemental refrigerationprocess is rejected, and thru the outlet opening 516 and its respectiveexhaust port, pipe or stack 518 associated with condenser fan(s) 543.Condenser fan(s) 543, or their respective exhaust stacks, areimplemented with backdraft dampers 519 that prevent air from bypassingpre-filter 529 and pre-cooler 530, by reversal of flow when condenserfan(s) 543 and refrigeration is off. The back-draft dampers 519 alsoallow for fan staging for optimal control and minimum energyconsumption. The speed of fan(s) 543 may vary for control ofrefrigeration head pressure or to otherwise optimize the refrigerationprocess. The portion of the pre-cooled air leaving direct evaporativecooler 530 that flows thru the OS/A (scavenger) path of the air-to-airheat exchanger 550 to accomplish the IASE/RACU heat rejection iscontrolled by scavenger fan(s) 536 in the manner described aboveregarding the other embodiments. Each fan 536, or auxiliary exhauststack 518 is implemented with a back-draft damper 519 such thatscavenger fans 536 can be staged for optimal control as previouslydescribed in other embodiments. Back-draft dampers(s) 519 may be omittedon scavenger fan(s) 536 on systems using only one scavenger fan.

IASE/RACU 510 may include a filter 529, or an additional filter asappropriate, like filter 332 in IASE/RACU 310 shown in FIG. 3, to filterthe OS/A early in the cycle in this side of the IASE/RACU 510. Thespecific placement of the filter 529, or an additional filter, may beselected to filter the OS/A prior to the OS/A entering the directevaporative cooler 530 and/or the plate-type air-to-air heat exchanger550. As with the embodiment shown if FIG. 3, the filter may work inconjunction with, or separately from the direct evaporative cooler 530,or other pre-cooling device, that may be included in the OS/A pathtoward the air-to-air heat exchanger 550.

A unique capability of IASE/RACU 510 is that IASE and refrigerationprocesses may operate completely independently of one another. Heat fromR/A air flow entering through one or more R/A inlets 514 may beextracted by 100% IASE (thru the air-to-air heat exchanger 550 to theOS/A-EA cycle and be exhausted as E/A through the operation of one ormore scavenger fans 536), or 100% by refrigeration coil(s) 542, wherethe heat of compression is rejected to condenser coil 540, or by any mixof IASE and refrigeration. The refrigeration process is controlled byeither digital scroll or variable speed compressors, operating eithersolely, or in concert with, on/off compressors thru a vernier controlmethod.

FIG. 5 illustrates a cross-section depicting a sample counter-flow airflow of the air in the plate-type air-to-air heat exchanger 550 depictedin the IASE/RACU 510 shown in FIG. 4. FIG. 5 details the segregation ofthe various air paths, and the counter-flow design of the plate-typeair-to-air heat exchanger 550 components. R/A entering through inletopenings 514 that may be placed on top of, or on an upper side of, theIASE/RACU 510 passes in down through the air-to-air plate-type heatexchangers 550 and exits out the bottom of the heat exchangers 550 whereit may either discharge from the unit out the bottom, or flow toward thesupply outlet 512, where in so passing it may be further cooled byrefrigeration coils 542 as appropriate to control the target supplytemperature of the S/A. Cooling coils 542 may optionally be installedbelow the heat exchangers 550. This counter-flow design provides forOS/A to enter the air-to-air heat exchanger 550 through inlet openings520 generally at a bottom, bottom side, or substantially along an entireside, of the IASE/RACU 510. The OS/A is pulled, generally by thescavenger fans 536, and condenser fans 543, at or near the exhaustoutlet openings 516 and exhaust ports, pipes or stacks 518, upward andcounter flow to the R/A, through the plate-type air-to-air heatexchangers 550 to exit as E/A via outlet openings 516 and exhaust ports,pipes or stacks 518 from the air-to-air heat exchangers 550 and theIASE/RACU 510, optimally including back-draft dampers 519.

FIG. 6 illustrates a third exemplary embodiment of an IASE/RACU 610using a cross flow heat exchanger according to this disclosure. The heatexchanger 650 may be constructed of polymer tubes, polymer plates, ormetallic plates, however this discussion is centered on use of thepolymer-tube type heat exchanger. In this embodiment, the air-to-airheat exchanger 650 is slightly modified in the manner described below.R/A enters generally through an inlet 614 and is moved by circulatingfan, or fans, 638 toward the air-to-air heat exchanger 650. In thisembodiment, polymer tubes are oriented horizontally, with the R/Aflowing inside the tubes through the air-to-air heat exchanger 650. OS/Aenters the IASE/RACU 610 through an inlet, or inlets 620, that mayoptionally include a filter 632 placed at or downstream of the inlet, orinlets 620 in the airflow direction, to be drawn generally verticallythrough the air-to-air heat exchanger 650 and around the exterior of thepolymer tubes through which the R/A is made to flow internally throughthe action of the circulating fan(s) 638. Movement of the OS/A isfacilitated by scavenger fan, or fans 636, placed in exhaust ports,pipes or stacks 618 generally in proximity to an exhaust outlet opening616. The scavenger fans 636 draw the E/A out of the top of theair-to-air heat exchanger 650.

An additional water spray manifold 655, and mist eliminator 657, may beprovided to facilitate spraying an evaporating water film onto theexterior of the polymer tubing in the air-to-air heat exchanger 650. Aswas shown in other embodiments, an additional cooling coil 642 may beprovided to further cool the S/A leaving the IASE/RACU 610 via outletopening 612 to be returned to the cold aisles of the data center asshown in FIG. 1. In addition, if mechanical cooling is used then it isadvantageous from a refrigeration efficiency standpoint to use the oftencooler, moist scavenger air leaving the heat exchanger to reject heatfrom the condenser coil 659 as shown in FIG. 6.

In the horizontal polymer-tube IASE/RACU 610 of this embodiment, anelliptical shape of heat exchanger tubes may maximize the allowablesurface area for heat rejection. Polymer tubing is used that issufficiently elastic such that subtle expansion and contractionresulting from pressure increases and decreases within the tubesaccording to normal operation of the IASE/RACU 610 will aid in sheddingresidual solids from the polymer tubes that may form as a by-product ofevaporation. With OS/A flowing over an exterior wet tube surface,evaporative heat transfer results in additionally efficient cooling ofthe air in the R/A-S/A side of the heat exchanger in order that the R/Afrom the hot aisles of the data center, as shown in FIG. 1, flowingthrough the inside of the polymer tubes, is efficiently cooled.

It should be recognized that such an air-to-air heat exchanger 650 couldbe operated dry, but there is a specific increase in efficiency when theoutside of the polymer tubes are wetted. Additionally, when comparingwet polymer-type heat exchangers to dry plate-type counter flow heatexchangers, advantages are further recognized that include (1) generallylower equipment costs, (2) reduced size and weight, (3) additionalenergy efficiency based, for example, on lower scavenger-side pressuredrop and corresponding required scavenger fan power, (4) a reduction inthe requirement to filter OS/A since water sprays continuously arewashing the scavenger side of the heat exchanger during operation withsprays on, and (5) polymers used in the construction of the tubing arecorrosion resistant. Against these advantages, certain disadvantagesneed to be evaluated for a specific application. These disadvantages arebased around greater consumption of water and the potential necessityfor non-chemical, or chemical based, water treatment systems. When theoutdoor air dry-bulb temperature is below approximately 35° F., thewater sump(s) 660 may be drained and the system may be operated dry toavoid freezing. The OS/A may be filtered prior to the heat exchanger650, by filters 632, thereby helping to keep the sump and circulatingwater system cleaner.

FIG. 7 illustrates an exemplary roof-top distribution of a plurality ofIASEs/RACUs 750, 755 according to this disclosure. As shown in FIG. 7, aplurality of appropriately-sized IASEs/RACUs 750, 755 may be placed on,for example, a rooftop of the data center to provide the required airflow to facilitate the disclosed cooling process.

As mentioned briefly above, substantial benefit of the systems andmethods according to this disclosure is the elimination of detailedfiltering methodologies which are required for other air conditioningsystem installations that may support a data center. In this regard,filters may be limitedly provided as appropriate in the SSFU discussedabove, or otherwise in less than all of the plurality of IASEs/RACUs750, 755. In a typical installation, for example, one in fiveIASEs/RACUs 750, 755 may include an additional filtering capability. Asshown in FIG. 7, the plurality of IASEs/RACUs 750, 755 may be dividedinto a plurality of zones 770 for a particular data center with aircleaning/particulate removal being accomplished by filters installed inthe middle row of each zone of IASEs/RACUs 750, 755, i.e., IASEs/RACUs750C, 755C for zone 770A, IASEs/RACUs 750H, 755H for zone 770B,IASEs/RACUs 750M, 755M for zone 770C, and so on. The combination of thefilters in the SSFU, and/or in a portion of the IASEs/RACUs 750, 755, isoptimized to afford appropriate filtration while maintaining theefficiency of the overall air handling system by not adversely impedingair flow through the system with additional unwarranted filtration.

It should be recognized that the systems and methods according to thisdisclosure are not limited to, for example, any particular installationsuch as that shown as a rooftop embodiment for IASEs/RACUs 750A-X, 755A-X in FIG. 7. The IASEs/RACUs 750, 755 could be, for example, mountedon pads on the ground adjacent to, or otherwise mounted in any manner tothe exterior or interior of, the building to facilitate, depending onconstruction of the building, their ability to intake OS/A and exhaustE/A away from the OS/A inlets while providing cooling of the R/A throughan air-to-air heat exchanger to provide S/A at the target air deliverytemperature, to the cold aisles of the data center shown in FIG. 1.

C. Side-Stream Filtration Unit (SSFU)

FIG. 8 illustrates a schematic diagram of an exemplary embodiment of aSide Stream Filtration Unit (SSFU) 140 according to this disclosure. Asshown in FIG. 8, an SSFU 140 may include an A/A inlet opening 142 viawhich, for example, a conduit 138 from a MUAD/HU 130 as shown in FIG. 1may provide A/A. R/A is drawn into the SSFU 140 via inlet opening 144.As indicated above, an objective may be for filtration/particulateremoval of RIA from the space at a volumetric exchange rate of, forexample, 6-10 air exchanges per hour, augmented by optional polishingfiltration of A/A in the SSFU. Air flow through the SSFU 140 may becontrolled by a variable speed circulating fan 810 that draws theoptional A/A and R/A, admitted as indicated, through the SSFU 140,including through one or more air filters 820. The air filters 820 ofthe SSFU 140 may be of any composition that best facilitates filteringthe air, including pleated filters, final filters up to HEPA grade, gasphase filtration units, electrostatic filtration units, and the like.The use of an SSFU 140 in the manner described allows particulate andgaseous substances to be removed from data center RIA, while avoidingthe necessity to volumetrically filter all of the air passing into andout of the IASEs/RACUs 110, as shown in FIG. 1 Removing the need tofilter all of the air saves, for example, significant circulating fanmotor horsepower. A filtered combination of optional A/A and R/A, afterpassing through air filters 820 under the control of variable speedcirculating fan 810, may exit the SSFU 140 via outlet 146 as SF/A to bere-merged, e.g., via a conduit 122 with the larger volume of R/A flowingto the plurality of IASEs/RACUs 100 via the R/A plenums 156 (as shown inFIG. 1), or simply back into the room.

D. Make-Up Air Dehumidification/Humidification Units (MUAD/HU)

FIG. 9 illustrates an exemplary embodiment of a Make-Up AirHumidification Unit (MUA/HU) 930 according to this disclosure, as anexample of the MUAD/HU 130 shown in FIG. 1. As shown in FIG. 9, anexemplary embodiment of an MUA/HU 930 may include an OS/A inlet opening932, that may include an intake hood (not shown), through which OS/A isdrawn into the MUA/HU 930. A roughing, e.g. metal mesh, pre-filter 910may be employed over the inlet opening 932 of the MUA/HU 930. R/A may bedrawn into the MUA/HU 930 via inlet opening 935, via R/A damper 990 tocontrol the flow of R/A into the MUA/HU 930 based on climatologicalconditions to facilitate other (heating/humidifying) operations of theMUA/HU 930. A heat pipe 915 may be provided to facilitate pre-heatingthe OS/A (temperature equalizing of the OS/A and R/A prior to mixing)when the OS/A damper 920 associated with the heat pipe 915 is open toadmit the OS/A through the MUA/HU 930. Air flow through the MUA/HU 930is facilitated by fan 940. The OS/A may be filtered by one or morefilters, for example, including a pre-filter 911 followed by a finalfilter 912. With evaporative humidifier pad face and bypass dampers, 960and 950 respectively, air flow humidification can be controlled througha humidifier 970. A mist eliminator 980 may be installed after theevaporative humidifier pad of the humidifier 970 to attempt to ensurethere is no carry-over of water droplets into the A/A airstream exitingthe MUA/HU 930 via outlet opening 934. When more humidification isrequired, the face damper 960 is modulated more open while the bypassdamper 950 is modulated more closed. Alternatively, when lesshumidification is required the face damper 960 is modulated more closedwhile the bypass damper 950 is modulated more open. In this manner, theA/A output from the MUA/HU 130 via outlet opening 934 may beappropriately humidified.

The exemplary embodiment of a MUA/HU 930 shown in FIG. 9 is unique in anumber of advantageous aspects. First, the exemplary MUA/HU 930 affordsan ability to precisely control humidification with no external heatsource. All of the heat for the humidification process is derived fromthe R/A of the data center itself. Second, removal of the intakeroughing filters 910 during winter operation, allows the design toprovide for OS/A entry without restriction even during extreme snow,icing, hoar frost, and other winter extremes. The heat pipe 915transfers heat from the data center R/A to pre-heat the OS/A well abovefreezing. This pre-heating of the OS/A allows for the mixing of OS/A andR/A airstreams without, for example, risk of forming ice crystals priorto humidification and attempts to ensure that the mixed air wet-bulb iswell above freezing prior to the adiabatic humidification process.Third, the heat pipe 915 may have an offset partition so as to allow forgreater RIA air flow relative to OS/A air flow, without imposing excesspressure drop. In extreme cold climates, the R/A air flow may bemaintained advantageously up to three times the air flow of the OS/A toachieve a desired OS/A pre-heating and humidification. Fourth, the heatpipe 915 may be installed sloped, as shown in FIG. 9, completelyvertical with the warm return flowing over the lower tube fins, orhorizontal as optimal for any design constraints and climatologicalconditions. Fifth, filtration of only the OS/A fraction by one or morefilters such as those depicted as elements 910, 911 and 912 in FIG. 9,allows for the use of smaller filters resulting in lower cost and allowsthe R/A over the heat pipe 915 to incur commensurate pressure drop tothe combined total pressure drop of the OS/A path without impacting thefan motor power. Finally, OS/A flow may be kept constant as filters loadby implementing an air flow measurement device in the OS/A path, whichmay be accomplished by correlation of the OS/A air flow rate withpressure drop over the heat pipe 915, and modulating the OS/A damper 920and/or speed of the fan 940 to maintain the appropriate air flow value.Alternatively, the OS/A damper 920 may modulate for control of buildingpressure.

It should be noted further that the use of a parallel flow heat pipe togain process advantage in the means detailed is an additional uniquefeature of the exemplary MUA/HA 930 shown in FIG. 9.

FIGS. 10-12 (in multiple plan views and a single elevation view)illustrate a second exemplary embodiment of a Make-Up AirDehumidification/Humidification Unit (MUAD/HU) 1030 according to thisdisclosure. As shown in plan views in FIGS. 10 and 11, an exemplaryembodiment of a MUAD/HU 1030 includes a winter (humidification) OS/Ainlet opening 1032A and a summer (dehumidification) OS/A inlet opening1032B, each of which may include an intake hood, by which OS/A is drawninto the MUAD/HU 1030 during the respective humidification ordehumidification mode of operation according to climatologicalconditions and seasons. An OS/A pre-filter 1011 may be employed at thesummer OS/A inlet opening 1032B of the MUAD/HU 1030. R/A may be drawninto the MUAD/HU 1030 via inlet opening 1035, via R/A damper 1090 tocontrol the flow of R/A into the MUAD/HU 1030 based on climatologicalconditions to facilitate other (heating/humidifying) operations of theMUAD/HU 1030. A heat pipe 1015 may be provided to facilitate pre-heatingthe OS/A (temperature equalizing of the OS/A and R/A prior to mixing)when a winter OS/A damper 1020A is open to admit the OS/A through theMUAD/HU 1030 during a humidification mode operation. Air flow throughthe MUAD/HU 1030 is facilitated by ventilation fan 1042 andrecirculation fan 1044. MUAD/HU 1030 may include a humidifier 1070 and adehumidification coil 1035. MUAD/HU 1030 may also include on-boardrefrigeration 1095 (air or water cooled, see FIG. 12) to facilitate thedehumidification process. Ventilation fan 1042 may include an air flowmeasuring device and controls to maintain constant flow of air under alloperating modes. Ventilation air fan 1042 and recirculation air fan 1044motors may include variable speed control devices.

Details of a Winter (Humidification Mode) for the exemplary embodimentof the MUAD/HU 1030 depicted in FIGS. 10-12 will now be described withspecific reference to FIG. 10.

During winter (humidification mode) operation, OS/A air enters theMUAD/HU 1030 via OS/A inlet opening 1032A through winter OS/A damper1020A. The OS/A flows through final filter 1012, inactive dehumidifyingcoil 1035, and heat pipe 1015 (where the OS/A receives preheat energyfrom R/A), pulled by ventilation fan 1042 into mixing chamber 1060.Summer transfer damper 1025 is closed during humidification modeoperation. Ventilation fan 1042 may speed up, or slow down, as requiredto maintain constant ventilation air flow or room pressure. R/A damper1090 opens, allowing R/A to flow through heat pipe 1015 and impart heatto the cooler OS/A flowing over the opposite side of the heat pipe 1015.RIA is pulled by recirculation air fan 1044, through recirculation airisolation damper 1027 (which may be a motorized or back-draft type) intomixing chamber 1060, where the RIA blends with the OS/A. The mixture ofOS/A and R/A flows through humidifier 1070, where moisture is added intonow mixed A/A prior to exiting the MUAD/HU 1030 via outlet 1034.Humidification is controlled by varying the speed of recirculation airfan 1044. On a call for more humidification, recirculation fan 1044speeds up for greater flow of warmed R/A. On a call for lesshumidification recirculation fan 1044 slows down. A mist eliminator 1080(see FIG. 12) may be installed after the evaporative humidifier pad ofthe humidifier 1070 to attempt to ensure there is no carry-over of waterdroplets into the A/A airstream exiting the MUAD/HU 1030. In thismanner, the A/A output from the MUAD/HU 1030 via outlet opening 1034 maybe appropriately humidified.

Details of a Summer (Dehumidification Mode) for the exemplary embodimentof the MUAD/HU 1030 depicted in FIGS. 10-12 will now be described withspecific reference to FIG. 11.

During summer (dehumidification mode) operation, OS/A enters the MUAD/HU1030 via OS/A inlet opening 1032B through summer OS/A damper 1020B. TheOS/A flows through pre-filter 1011 prior to entry into the MUAD/HU 1030.The OS/A flows through pre-cool path of optional heat pipe 1015, throughthe summer transfer damper 1025, through final filter 1012, into activedehumidifying coil 1035, where moisture is extracted as controlled bymodulation of a chilled water valve or staging/modulating compressorswhen on-board refrigeration is employed, and finally through the reheatpath of optional heat pipe 1030 (where it receives reheat energy fromwarmer OS/A and imparts beneficial pre-cooling to the OS/A). Thispre-cool air reheat cycle, as defined by ASHRAE, is well defined in theHVAC industry and is sometimes referred to as a “Wringer” cycle. Duringdehumidification mode, recirculation damper 1090 is closed,recirculation isolation damper 1027 is closed, and recirculation fan1044 is off. Ventilation air is pulled by ventilation fan 1042, where itpasses through inactive humidifier 1070 to A/A outlet 1034. In thismanner, the A/A output from the MUAD/HU 1030 via outlet opening 1034 maybe appropriately dehumidified as required for control of room dew pointor relative humidity. The pre-cool air reheat cycle may save typically25% to 50% of the cooling/dehumidification energy that would otherwisebe required.

The exemplary embodiment of a MUA/HU 1030 shown in FIGS. 10-12 is uniquein a number of advantageous aspects. First, MUAD/HU 1030 affords theability to precisely control humidification, by variable recirculationflow controlled by recirculation fan 1044 with no external heat source(all heat for the humidification process is derived from the data centeritself from the warm R/A airstream). Second, the heat pipe 1015transfers heat from the data center R/A to pre-heat the OS/A well abovefreezing. This pre-heating of the OS/A allows for the mixing of OS/A andR/A airstreams without risk of forming ice crystals prior tohumidification and ensures that the mixed air wet-bulb is well abovefreezing prior to the adiabatic humidification process. Third, the heatpipe 1015 may have an offset partition to allow for greater R/A airflows relative to OS/A air flows, without imposing excess pressure drop.In extreme cold climates, the R/A air flow may be maintainedadvantageously up to three times the air flow of the OS/A to achieve adesired humidification. Fourth, the heat pipe 1015 may be installedsloped, with the lowest point in the recirculation/pre-cool path of theheat pipe 1015 or horizontal as optimal for any design. Fifth,filtration of only the OS/A fraction allows for smaller filtersresulting in lower cost. Sixth, OS/A flow may be kept constant asfilters load by implementing an air flow measurement device on the OS/Afan (for example a piezometer ring installed at the fan 1042 inlet witha pressure transmitter). Finally, the heat pipe 1015 is used to benefitin both dehumidification and humidification modes in a unique way.

E. Method For Controlling High Internal Heat Gain Recirculated AirCooling System

It should be appreciated that the various components shown in FIG. 1,for example, allow for precise control of the heat dissipation,particulate removal, air quality, and humidity levels within the datacenter. The precise control is based on individual control methodologiesfor the independent components, and specifically on control of the flowrates of air through both sides of the IASEs/RACUs for the heatrejection process. The individual control methodologies can besynchronized among any combination of the components based on measuredconditions internal and external to the data center. Inputs and feedbackmay be provided by sensors located within the data center, within theindividual components, or within the external environment.

Computer controlled optimization may be undertaken according to a numberof methodologies for most efficiently managing the cooling through theplurality of IASEs/RACUs supporting a specific data center. For aspecific horizontal elliptical profile polymer-tube type air-to-air heatexchanger, as shown in FIG. 6, mathematical modeling has led to thederivation of Equation 1 that approximates the Wet Bulb DepressionEffectiveness (WBDE) and may potentially be used to advantage forcontrolling the IASE/RACU.

WBDE≈(−0.0009t ²+0.0758t+16.158)ln(m _(w) /m_(d)+0.29t−0.3(t−t*)+52  (Equation 1)

where:

-   -   t is OS/A dry-bulb temperature in degrees Fahrenheit;    -   t* is OS/A wet-bulb temperature in degrees Fahrenheit;    -   m_(w) is mass flow rate of OS/A entering the air-to-air heat        exchanger in pounds dry air per hour;    -   m_(d) is mass flow rate of hot aisle R/A entering the heat        exchanger measured in pounds dry air per hour; and    -   WBDE is resolved as a percentage.

Equation 1 is essential for energy modeling because it allows forcomputation of mass flow of OS/A required to cool the RIA to a targetdelivery temperature given any OS/A dry-bulb and wet-bulb conditions. Asan example, given a RIA temperature (after an addition of approximately1.5° F. heat added by operation of the recirculating fan yielding 101.5°F. R/A at, for example, 55° F. dew-point, and ambient OS/A conditions of58° F. dry-bulb temperature and 51° F. wet-bulb temperature, the firststep is to compute the WBDE necessary to achieve a target supplycondition (assume 75° F.) according to Equation 2 below.

t _(s) =t _(r)−WBDE(t _(r) −t _(wb))  (Equation 2)

where:

-   -   t_(s) is the temperature of the target S/A (in this example, 75°        F.);    -   t_(r) is the temperature of the RIA (in this example, 101.5°        F.);    -   t_(wb) is the local outside wet-bulb temperature (in this        example, 51° F.);

Substituting the above values, the computed WBDE in this example is0.525. This represents the air-to-air heat exchanger WBDE that isrequired to cool the R/A to the target S/A condition. Substituting thiscomputed WBDE into Equation 1, it is a simple matter to compute therequired mass flow ratio of OS/A to R/A. In the example given, solvingEquation 1 would result in a determination that OS/A mass flow rate isrequired to be 44% of R/A mass flow rate.

While equations 1 and 2 are required for energy modeling, theIASEs/RACUs control discharge air temperature by varying the speed of,and/or staging scavenger fans in concert with controlling supplementalcooling coils as previously described

It should be recognized, based on the above equations, that as WBDEdeclines and required OS/A flow is reduced, the scavenger fans in theOS/A-E/A side of the IASE/RACU can operate at a lower capacity whilemaintaining the required temperature of the S/A to the data center.

As indicated above, S/A temperature is principally controlled by varyingOS/A scavenger air flow. Such control can be executed in a number ways.When, for example, ambient wet-bulb temperature is high, scavenger fansin the OS/A-E/A side of the IASE/RACU may run at 100% of design, toachieve maximum heat rejection. In such conditions, additional coolingfrom, for example, direct expansion refrigeration cooling, as aredescribed in certain of the embodiments of the IASE/RACU systems above,may be required. An advantage in a polymer-tube air-to-air heatexchanger-based IASE/RACU system, as shown, for example, in FIG. 6 isthat the scavenger fans in the OS/A-E/A side of the IASE/RACU can besized up to 50% more than rated flow. A consequent advantage of thissizing is that less incremental power may be required relative torefrigeration-based cooling to achieve equivalent heat rejection.

Scavenger fan motors that pull the OS/A through the air-to-air heatexchanger in the IASE/RACU are, therefore, generally equipped withvariable speed controls. These variable speed controls permit operationthat controls flow rate of OS/A as appropriate in order that S/A flowfrom the IASEs/RACUs can be carefully matched to the requirements fortemperature control in the data servers of the data center. Supply fanmotors also are generally equipped with variable speed controls, andsupply fan flow is regulated generally to match the flow of air pulledby the server fans by various control algorithms.

The algorithms required for control of the supply air temperature andflow are readily programmed into modern direct digital controllers orPLCs.

While this disclosure describes a number of specific embodiments, it isevident that many alternatives, modifications and variations will beapparent to those skilled in the art. Accordingly, the exemplaryembodiments set forth in this disclosure are intended to beillustrative, not limiting. For example, various other IASE/RACU designsschematically equivalent to the arrangement detailed in FIGS. 4 and 5are illustrated FIGS. 13-17, based on an assortment of other plate-typeheat exchanger and heat pipe options. In particular, FIGS. 13-17illustrate schematic diagrams of third through seventh exemplaryembodiments of IASE/RACU designs including the assortment of heatexchangers. FIG. 13 illustrates a schematic diagram of a third exemplaryembodiment of an IASE/RACU design including a vertical dual cross-flowplate-type heat exchanger arrangement. FIG. 14 illustrates a schematicdiagram of a fourth exemplary embodiment of an IASE/RACU designincluding a horizontal dual cross-flow plate-type heat exchangerarrangement. FIG. 15 illustrates a schematic diagram of a fifthexemplary embodiment of an IASE/RACU design including a vertical counterflow plate-type heat exchanger arrangement. FIG. 16 illustrates aschematic diagram of a sixth exemplary embodiment of an IASE/RACU designincluding a horizontal heat pipe heat exchanger arrangement. FIG. 17illustrates a schematic diagram of a seventh exemplary embodiment of anIASE/RACU design including a vertical heat pipe heat exchangerarrangement. In each of the depicted arrangements of FIGS. 13-17, basedon the assortment of other plate-type heat exchanger and heat pipeoptions, like features are addressed with similar nomenclature. In FIGS.13-17, R/A circulating fans are respectively referred to as elements1338, 1438, 1538, 1638 and 1738. Scavenger fans are respectivelyreferred to as elements 1336, 1436, 1536, 1636 and 1736. Condenser fansare respectively referred to as elements 1343, 1443, 1543, 1643 and1743. Back draft dampers associated with both scavenger fans andcondenser fans are respectively referred to as elements 1319, 1419,1519, 1619 and 1719. Refrigeration coils are respectively referred to aselements 1342, 1442, 1542, 1642 and 1742. Directive evaporative coolersare respectively referred to as elements 1330, 1430, 1530, 1630 and1730. OS/A filters are respectively referred to as elements 1329, 1429,1529, 1629 and 1729. Condenser coils are respectively referred to aselements 1340, 1440, 1540, 1640 and 1740. The individually depicted heatexchangers are respectively referred to as elements 1350, 1450, 1550,1650 and 1750. These various arrangements are depicted as additionalexemplary embodiments of potential flow designs intended to beencompassed by this disclosure.

It will be appreciated that various of the above-disclosed features andfunctions, or alternatives thereof, may be desirably combined intodifferent systems or applications. Also, various alternatives,modifications, variations or improvements may be subsequently made bythose skilled in the art, and are also intended to be encompassed by thefollowing claims. As such, various changes may be made without departingfrom the spirit and scope of this disclosure as defined in the claims.

1. An air cooling device, herein named an Indirect Airside Economizer(IASE) comprising: at least one air-to-air heat exchanger for exchangingheat between a primary recirculation air flow path and a secondaryoutdoor air flow path; an outside air pre-cool section, located in thesecondary outdoor air flow path, including at least one pre-cooler; arefrigeration condenser/heat rejection coil positioned on a downstreamside of the outside air pre-cool section; at least one condenser fanthat pulls pre-cooled outdoor air through the refrigerationcondenser/heat rejection coil; at least one scavenger air fan that pullspre-cooled outdoor air through the at least one air-to-air heatexchanger via the secondary outdoor air flow path; and at least onerecirculation air fan that recirculates primary air from an enclosedspace for the purpose of rejecting heat, the secondary outdoor air flowpath including an outside air inlet through which outside air is drawninto the outside air pre-cool section including the at least pre-cooler,the secondary outside air taking on two flow paths, a first flow pathpassing through the refrigeration condenser/heat rejection coil with acondenser outlet opening on an exhaust side of the refrigerationcondenser/heat rejection coil that includes the at least one condenserfan for exhausting heated air from the refrigeration condenser/heatrejection coil, and the second air flow path passing through one side ofthe at least one air-to-air heat exchanger via the secondary outside airflow path into an exhaust outlet by which the outside air, havingextracted heat from the recirculating air from the enclosed space, therecirculating air flowing through another side of the at least oneair-to-air heat exchanger via the primary recirculation air flow path,is exhausted by the at least one scavenger air fan positioned on anoutlet side of the air-to-air heat exchanger in the secondary outdoorair flow path, and the primary recirculation air flow path including areturn air inlet through which warm return air from the enclosed spacewith high internal heat generation is drawn, by means of the at leastone recirculation air fan, through the at least one air-to-air heatexchanger, followed by the refrigeration evaporator/cooling coil and asupply outlet via which the cooled recirculation air is supplied back tothe enclosed space as supply air at a temperature as appropriate forequipment located within the enclosed space.
 2. The air cooling deviceaccording to claim 1, wherein the enclosed space is a computer datacenter including multiple computer data servers and ancillary supportdevices, and the supply air is circulated through the multiple computerdata servers to extract the heat generated by the servers.
 3. The aircooling device according to claim 1, wherein the warm return air ismoved through the at least one air-to-air heat exchanger for the purposeof extracting heat.
 4. The air cooling device according to claim 1,wherein the pre-cooler located in the secondary air flow path is adirect evaporative cooler.
 5. The air cooling device according to claim1, wherein the refrigeration condenser/heat rejection coil serves toreject heat from the auxiliary refrigeration cooling system.
 6. The aircooling device according to claim 1, further comprising a refrigerationevaporator/cooling coil in the primary recirculation air flow pathbetween an outlet side of the air-to-air heat exchanger and the supplyoutlet.
 7. The air cooling device according to claim 1, furthercomprising back-draft dampers on the at least one scavenger air fan,when the at least one scavenger air fan comprises a plurality ofscavenger fans.
 8. The air cooling device according to claim 1, furthercomprising back-draft dampers on the at least one condenser fan, whenthe at least one condenser fans comprises a plurality of condenser fans.9. The air cooling device according to claim 1, wherein the temperatureat which the recirculation supply air exits the air cooling device iscontrolled by adjusting an air flow rate in the secondary outdoor airflow path.
 10. The air cooling device according to claim 1, wherein thetemperature at which the recirculation supply air exits the air coolingdevice is controlled by staging or modulating refrigeration basedsupplemental cooling when the scavenger air flowing through thesecondary outdoor air flow path through the at least one air-to-air heatexchanger is insufficient to extract all of the heat required.
 11. Theair cooling device according to claim 1, wherein an air-to-air heatexchange process and an active refrigeration process are operatedcompletely independently of one another.
 12. The air cooling deviceaccording to claim 1, wherein the at least one scavenger air fan is avariable speed fan, and the secondary outdoor air flow is adjusted byvarying the speed of the at least one variable speed scavenger air fan.13. The air cooling device according to claim 1, wherein the at leastone scavenger air fan is a plurality of scavenger air fans, and thesecondary outdoor air flow is adjusted by cycling on and off at leastone of the plurality of scavenger air fans to achieve optimal efficiencyin concert with modulating the speed of at least one other of theplurality of scavenger air fans operating to reject the heat.
 14. Theair cooling device according to claim 1, wherein the at least oneair-to-air heat exchanger comprises at least one of the following: a) avertical or horizontally arranged dual cross-flow plate-type heatexchanger, b) a counterflow plate-type heat exchanger, or c) ahorizontal or vertical heat pipe heat exchanger.
 15. The air coolingdevice, according to claim 1, wherein the secondary air flow pre-coolerprovides advantage for rejecting heat from the primary airflow throughthe air-to-air heat exchanger(s) and the refrigeration condenser. 16.The air cooling device according to claim 1, wherein the air-to-air heatexchanger is at least one of constructed of polymer tubes, polymerplates, or metallic plates.
 17. The air cooling device according toclaim 16, further comprising: an additional water spray manifold, andmist eliminator to facilitate spraying an evaporating water film ontothe exterior of the polymer tubing in the air-to-air heat exchanger. 18.The air cooling device according to claim 17, wherein moist scavengerair leaving the heat exchanger is used to reject heat from the condensercoil.
 19. The air cooling device according to claim 17, wherein the atleast one air-to-air heat exchanger can be operated dry.
 20. The aircooling device according to claim 1, wherein the at least one air-to-airheat exchanger can be operated dry, without use of evaporative coolingmeans.